Are Native Plant Gardens better for conserving bird populations than Gardens with exotic plants? Jessica Ann Gouveia Department of Biology and Psychology, University of Connecticut ABSTRACT Loss of species habitat due to rapid deforestation of the e This issue especially affects birds. One way in which scientists and conservationists have suggested people could help conserve bird populations is by gardening. Many horticulturalists want to bring in orn amental exotic species of plants, however, it is believed by some that they offer little contribution to a functional ecological system; they do not harbor as many insects, nor do they have an ecological history with the birds of the native habitat. In thi s study, I examine the issue of whether native plants offer better habitats for bird conservation by comparing the birds that visit the native garden at the Biological Station of Monteverde (EBMV), an exotic garden at Los Pinos, and a mixed species garden at El Bosque. After comparing the different birds that visited each of these gardens and dividing them into categories based on their preferred habitat, I did not find a difference in the number of species that visited each garden, but I did find a differe nce in the type of species that I found. Overall, I found that the native plants support bird populations with more specialized habitats better than exotic plants do. At one point, the entire region of Monteverde was covered by primary forest. All of its savannas and grasslands have been created by human activity (Nadkarni & Wheelwright 2000). For example, the dry, open area along the road to Monteverde, from the Inter American Highway, is kept up by burning, clearing, and cattle grazing. As deforestation persists throughout Central America, and in Monteverde, a lot of bird species are threatened because of loss of habitat and food sources (Nadkarni & Wheelwright 2000). Scientists and conservationists are constantly thinking of ways to offset the damages of deforestation (Foley et al. 2005). One idea that has been suggested to help conserve bird populations is to make the best of already disturbed areas by turning them into native plant dominated gardens, and by turning current gardens into native plant d ominated areas (Tallamy 2009). Douglas Tallamy, 2009, suggests that although some species need primary forest and could never live in disturbed areas, many birds would benefit from a well designed garden of native plants. Along the lines of this idea, gard eners would aim to imitate the habitat that has been cut down by using native species to replicate what has gone missing in food and shelter. The idea is that this would better support bird communities than a patch of grass or any human constructed structu re would (Tallamy 2009). However, there is conflict in the world of gardening between the proposal of using native species to support birds and the idea of planting for aesthetic pleasure. A large community of horticulturalists want to bring new, alien pl ants into the natural environment (Reichard & White 2001). Although some exotic plants serve a medicinal purpose, a lot of exotic species have been imported and planted for purely ornamental purposes (Reichard & White 2001) However, it is thought that exo tic species offer little to a functioning ecological system. For example, they do not harbor a large or diverse
population of insects; insects will not eat them (Tallamy 2009). This is because most horticulturalists choose pest free plants so that their ga rden will stay intact and pretty. Also, insects have to develop and adapt to the chemical defenses of plants ( Reichard & White 2001) So, if a new species of plant is introduced with a new poison in its leaves, the insect will not be well adapted to feed o n it; it needs an evolutionary history with the plant (Tallamy 2009). populations; planting native species is a way to mimic what is lost by deforestation by bird populations, and exotic plants offer little support for a major food source for birds (insects). The aim of this project was to determine if an area of native plants actually makes for a better habitat for birds than an area full of exotic species. I compared bird spe cies composition at a native, an exotic, and a mixed species plant garden to determine which is better for bird conservation and why. MATERIALS AND METHODS Figure 1. Shows maps of each of the gardens I observed in Monteverde, July, 2008. Part i.) was Study sites This research was conducted in three gardens around Monteverde, Costa Rica, in the premontane wet forest life zone. The three gardens were the Biological Station of Mondeverde (EBMV1 & EBMV2), Los Pinos, and El Bosque, a native plant dominated garden, an exotic plant dominated garden, and a mixed species plant garden, respectivel y. Note that the Biological Station of Monteverde served as both EBMV and
EBMV2. It was the same garden. The two different notations represented the two different weeks that it was sampled. Table 1. Shows the type of plant species that were present in c ertain sections of the gardens I observed in Monteverde, July, 2010, and whether they were native or exotic. The garden at the Biological Station was approximately 1,084 m 2 About 5% of area A of Figure 1 consisted of cement for pathways. 25% of the are a was constituted by trees including a few native trees: Quercus insignis of the Fagaceae family, Psidium guajava of the family Myrtaceae, and Conostegia Xalapensus, of the family
Melastomataceae. There was also a nonnative tree, Eriobotrya japonica of the family Rosaceae, which made up 20% of the trees. This area also included many native plants (for full description of these plants, see Table 1). Part B of the figure consisted of grass, and part C was dominated by the exotic species Hibiscus rosasinens is, of the Malvaceae family. The garden at Los Pinos was approximately 2,413 m 2 Referring to part ii of Figure 1, part A made up approximately 10% of the garden. It was dominated by the exotic tree species Dypsis lutescens, of the family Arecacea Part B made up approximately 20% of the garden. It was dominated by the exotic species Cupressus Lusitanica of the Cupressaceae family. Other trees mixed in this part included the native species Citharexylum costaricensis, of the family Verbenaceae family, and Persea Americana of the Lauraceae family Part C consisted of some scattered trees, plants, and shrubbery amongst grass (for full description of composition, see Table 1). Part D was made up of cabins. It made up about 17% of the garden. This part also had a few cement pathways, which made up about 5% of the garden. Surrounding the garden were more gardens, cabins, and a driveway. El Bosque was approximately 2,104 m 2 Referring to Figure 3, the part labeled A took up 1/4 th of the part A and part B combine d. It was completely constituted by trees, about 85% of which were native. These native trees included the species: Tapirira mexicana of the Anacardiaceae family (which was the most common), Viburnum costaricanum Ehretia latifolia Cinnamomum sp ., Roupala sp ., Quercus brenesii Ficus benjamina Myccia splendens Eugenia montevidensis and a tree in the Myrtacaea family. The non native trees i ncluded the species: Arial batria Jacaranda mimosifolia and Syzygium jambos The part labeled B in Figure 1 was made up of grass. 1/3 of part C consisted of non native trees, of which the majority were Ficus benjamina, of the Moraceae family The other 2 /3 of this section was split between native and non native shrubbery, plants, and some trees (See Table 1 for full description). Forest surrounded part of the garden, and cabins surrounded the majority of the garden. Study design To assess whether more b irds visit native gardens than exotic gardens, I visited the three aforementioned study sites in an alternating pattern. The time frame of my project was two weeks. In the first week, I visited Los Pinos and EBMV. On day one, I started bird watching at 7:0 0 A.M. at EBMV and ended at 8:30 A.M. That same day, I visited Los Pinos and bird watched there from 9:15 A.M. until 10:45 A.M. On day two, I started bird watching at 7:00 A.M. at Los Pinos and ended at 8:30 A.M. Then, in the same day, I visited EBMV and bird watched there from 9:15 A.M. until 10:45 A.M. I repeated this alternative schedule two times. So, I visited each garden four times that week. The second week I followed the same procedure, but with El Bosque and EBMV2. EBMV2 was the same garden as EBM V, but was referred to EBMV2 during the second week of sampling. Also, on day five, EBMV2 was not sampled. Birds were identified, while walking around the garden in a repetitive fashion. I found a route in each garden that covered the entire area, and wal ked that route continually. In order to find the similarities between the different gardens, I used the Sorensen Similarity Index.
RESULTS During my project, 21 species of birds were seen in EBMV, 23 in El Bosque, 20 Los Pinos, and 16 were seen during th e 2 nd week in EBMV2 (Table 1). According to Table 2, of these species the most amount of birds were shared between El Bosque and Los Pinos, and the least amount were shared between Los Pinos and EBMV2 and El Bosque and EBMV2. Note that one less day of sa mpling was done for EBMV2 than all the other gardens. TABLE 1. Representation of the number of days each species was seen in the different gardens in Monteverde, July, 2010 and the preferred habitats of each species. Obs represents the total number of da ys the species were seen in all. Table 2. Description of preferred habitats. Categories are arranged from least to most disturbed area.
_______________________________________ TABLE 3. Sorensen Similarity Index between three different gardens in the Monteverde Area, July 2010. The numbers left of the diagonal row of X's are the results of the Index. The numbers to the right of the X's represent the number of species of birds that the corresponding pairs of gardens have in common. Of the species that were shared between the EBMV gardens there were forest edge species and forest and open woodlands species. So, there were some species on either side of the line, which separated more disturbed areas from non disturbed areas (Fig. 2). In the graph co mparing both EBMV gardens and El Bosque, we see forest edge species again, as well as those species to the right of the line, in disturbed areas (Fig. 2). However, in comparing the EBMV gardens and the Los Pinos garden, we only see forest and open woodland species. Finally, the majority of species that exist in both El Bosque and Los Pinos preferred habitats that were categorized as more disturbed areas (Fig. 2). When comparing the species shared in all of the gardens, most were disturbed area species, some were forest and open woodlands species and only one of nine, the Gray breasted Wood Wren, lied to the left of the graph as an understory species (Table 1, Fig. 2). In analyzing which species were only seen in one garden during this period, it was found that all species lied to the left of the line in the graph (Fig. 3). In EBMV2 most species were in non disturbed areas, with the exception of two that preferred disturbed areas, the Bananquit and the White naped Brush finch (Table 1, Fig. 3). In El Bosque, there was a mix of species to the right and left of the line. However, most lied to the right, in more disturbed areas (Fig. 3). In Los Pinos, most lied to the right of the line (Fig. 3). Note that the species on the left side of the graph for El Bosque was an understory species, and the species on the left side of the graph for Los Pinos was a forest edge species (Fig 3). It is important to see the difference because in this study we are denoting forest edge as a less specialized habitat than the underst ory of mature forest.
FIGURE 2. This graph shows the preferred habitats of the birds that are shared between gardens of Monteverde, July 2010. These six categories are described in Table 2. Note that, as the categories move from left to right, the prefe rred habitats become less specialized and more disturbed as a result of human influence. The red line in this figure represents a division between more disturbed habitats and less disturbed habitats.
FIGURE 3. This figure shows the preferred habitats of the birds that were only seen in one place. This also shows the preferred habitats of the birds seen in EBMV, El Bosque, and Los Pinos. Note that here, EBMV and EBMV2 are considered the same location. Also, as the categories move from left to right, th e preferred habitats become less specialized and more disturbed as a result of human influence. The red line in this figure represents a division between more disturbed habitats (on the right) and less disturbed habitats (on the left).
DISCUSSION From t he fact that the total number of species found in each of the gardens are very similar, it can be concluded that there is little difference in the number of bird species found in native gardens, exotic gardens, and mixed gardens. However, my findings that the most number of birds were shared between El Bosque and Los Pinos, and the least number were shared between Los Pinos and EBMV2 and El Bosque and EBMV2 suggest that there could be a trend in the type of species that visit each garden. After categorizing the birds into groups based on the habitats they prefer, trends become evident (Flanders et al. 2006). When analyzing the data on which birds are shared between gardens and which habitats they prefer, we see a strong trend. We see that birds that can live in disturbed areas are found in every garden. This may be because they are well adapted to live in many different kinds of habitats, like gardens, forest, open woodlands, and plantations (Stiles & Skutch 1989). In contrast, birds that are more particular about the habitats they live in are absent in the graph showing the birds shared between all three garden sites with the exception of one species (Fig. 3). Birds that are more specialized in the habitats they prefer, like forest edge species, are seen i n the graph comparing the two EBMV gardens and the EBMV gardens and El Bosque (Fig. 2). However, forest species are absent in the graphs comparing EBMV with Los Pinnos and El Bosque with Los Pinos. This supports the idea that the more native dominated the garden, the more likely it is that you will see a bird that prefers a more specialized habitat. This idea is further supported by the figures showing the preferred habitats of the birds that are unique to each of the gardens. In the native garden, a lot o f species to the left of the line were seen (Fig. 3). There were also species to the right of the line in the native garden, which is not important because as aforementioned, those disturbed area species are well adapted for living in many different habita ts (Fig. 3). It is significant, however, that in the exotic garden, there were mostly species that are found in disturbed areas (Fig. 3). In the mixed garden, there were both species that were more specialized in their habitat selection and species that pr eferred disturbed habitat (Fig. 3). Native gardens, and in some cases, mixed gardens may be better able to support these more specialized species because they harbor more insects (Tallamy 2009). Again, this is because most horticulturalists choose pest free plants so that their plants avoid herbivory. Also, insects have to develop and adapt to the chemical defenses of plants ( Reichard & White 2001) So, there needs to be an evolutionary history between the plant and the insects, which is not present with exotic plants (Tallamy 2009). Also, many foods in Costa Rica are available in greater abundance and variety year round, so some species become specialized to certain fruits or to sucking nectar from certain flowers (Stiles & Skutch 1989). For example, be cause of their beaks, specialized hummingbirds need a certain curvature to the flowers they feed on (Stiles & Skutch 1989). This requires an evolutionary history between the birds and the flower, something that birds clearly lack with exotic plants (Stiles 1981). In contrast, less specialized birds, that can live in disturbed areas well, like the Bananaquit for example, can just pierce the flower and suck the nectar (Stiles & Skutch 1989). There were some limits to the sampling done in this experiment. I w as walking
around the garden; I may not have been able to see all the birds, especially if they were behind me, or at the opposite side of the garden as me. Also, physical structure of the habitat has been thought to be an important determinant of bird dis tribution (Rotenberry & Wiens, 1980). Since there were differences in the sizes and structures of the gardens, this might have played a roll in what species of birds visited them. It is believed that vertical vegetation is an important determinant of the s pecies present, and that the number of niches for birds increases with vegetative diversity (Block 1993). So the fact that there were different trees, with different heights and composition, and a different concentration of plants in each of the gardens, c ould have affected the number of niches available and therefore how many birds visited them. Based on this experiment, though, I believe that native plants make a garden better equipped to support birds that prefer more specialized habitats. Since distur bed area species do not seem to mind what kind of gardens they are visiting, we should plant with an aim to conserve more particular species. In this sense, I believe that exotic plants cannot contribute to a functional ecosystem in the same way that nativ e plants will. AKNOWLEDGEMENTS Thank you to Karen Masters for guiding me towards my project idea. Also, thank you to Pablo Allen for helping me to bird watch, for giving me field guides to reference, and for helping me analyze the data I collected. I sho uld thank Willow and Bill Zuchowski for helping me to identify all of the plants and trees in the gardens. Finally, I would like to send my gratitude to EBMV, El Bosque, and Los Pinos for allowing me to study in their gardens. LITERATURE CITED Block, W. M. & L.A. Brennan. 1993. The habitat concept in ornithology: Theory and applications. Current Ornothology 11 : 35 91. Nadkarni, N.M. & N.T. Wheelwright. 2000. Monteverde: Ecology and Conservation of a Tropical Cloud Forest. Oxford University Press, New Yor k, page 40. Reichard, S.H. & P. White. 2001. Horticulture as a Pathway of Invasive Plant Introductions in the United States. BioScience 51 :103 113. Rotenberry, J.T. & J.A. Wiens. 1980. Temporal variation in habitat structure and shrubsteppe bird dynamics Oecolgica 47 : 1 9. Stiles, F.G. 1981. Geographical aspects of bird flower coevolution, with particular reference to Central America. Ann Missouri Bot. Gard 68 : 323 351 Stiles, F.G. & A.F. Skutch. 1989. A Guide to the Birds of Costa Rica. Cornell Unive rsity Press, Ithaca. Tallamy, D.W. 2009. Bringing Nature Home: How You Can Sustain Wildlife with Native Plants. Timber Press, Inc., Portland.
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Gouveia, Jessica Ann
Son los jardines de plantas nativas mejor para la conservacin de las poblaciones de aves que los jardines con plantas exticas?
Are native plant gardens better for conserving bird populations than gardens with exotic plants?
Loss of species habitat due to rapid deforestation of the Earths forests is a pertinent and serious problem.
This issue especially affects birds. One way in which scientists and conservationists have suggested people could help conserve bird populations is by gardening. Many horticulturalists want to bring in ornamental
exotic species of plants, however, it is believed by some that they offer little contribution to a functional ecological system; they do not harbor as many insects, nor do they have an ecological history with the birds of the native habitat. In this study, I examine the issue of whether native plants offer better habitats for bird
conservation by comparing the birds that visit the native garden at the Biological Station of Monteverde (EBMV), an exotic garden at Los Pinos, and a mixed species garden at El Bosque. After comparing the
different birds that visited each of these gardens and dividing them into categories based on their preferred habitat, I did not find a difference in the number of species that visited each garden, but I did find a
difference in the type of species that I found. Overall, I found that the native plants support bird populations with more specialized habitats better than exotic plants do.
La prdida de hbitat de las especies debido a la rpida deforestacin de los bosques de la Tierra es un problema relevante y serio. Este problema afecta especialmente a las aves. Una de las formas en que los cientficos y los conservacionistas han sugerido que la gente podra ayudar a las poblaciones de aves es conservar la jardinera. Muchos horticultores desean traer especies ornamentales exticas de plantas, sin embargo, se cree por algunos que ofrecen poca contribucin a un sistema ecolgico funcional, que no albergan mayor cantidad de insectos, ni tampoco tienen una historia ecolgica con las aves del hbitat natural. En este estudio, se examina la cuestin de si las plantas nativas ofrecen mejores hbitats para la conservacin de las aves mediante la comparacin de las aves que visitan el jardn de plantas nativas en la Estacin Biolgica de Monteverde (EBMV), un extico jardn en Los Pinos, y un jardn de especies mixtas en El Bosque. Despus de comparar las diferentes aves que visitaron cada uno de estos jardines y dividindolos en categoras basadas en su hbitat preferido, no he encontrado una diferencia en el nmero de especies que visitaron cada jardn, pero he encontrado una diferencia en el tipo de especies que he encontrado. En general, me encontr con que las plantas nativas apoyan a las poblaciones de aves con hbitats ms especializados mejor de lo que las plantas exticas hacen.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Conservacin de la biodiversidad
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Summer 2010
Ecologa Tropical Verano 2010
t Monteverde Institute : Tropical Ecology